Mapping Dynamic Exposure: Constructing GIS Models of Spatiotemporal Heterogeneity in Artificial Stream Systems

Abstract

In flowing environments, the degree of turbulent flow determines the movement and distribution of chemicals. Variation in flow alters the patchiness of toxicant plumes within a stream ecosystem. This patchiness translates into variability in exposure pulses for organisms encountering the toxic plume. Throughout a stream, the processes that give rise to chemical plume structure will vary as a function of local flow characteristics. This research examines the influence of toxicant mode of entry and stream flow velocity on the spatiotemporal patterning of exposure. Two introduction treatments were evaluated: one mimicking groundwater and the other mimicking runoff. The influence of flow regime was examined through the comparison of models constructed under two stream flow velocities. Concentrations of a tracer molecule were recorded using an electrochemical monitoring system. From these localized, direct measurements, geographic information systems (GIS) were used to model exposure throughout the stream. Conceptualizing exposure as a series of toxicant pulses, exposure can be defined using a variety of chemical peak characteristics. Three-dimensional, layered maps were constructed defining exposure as the integrated area of toxicant peaks, the magnitude of peaks, and peak frequency. Differences in the spatial and temporal patterning of exposure were apparent both within treatments and between treatments. No two definitions of exposure yielded the same exposure distributions for any treatment. These models demonstrate that distribution of chemical exposure throughout a stream ecosystem is linked to both toxicant mode of introduction and iii stream hydrodynamics. Furthermore, these results demonstrate that optimal exposure modeling relies on first defining exposure. iv ACKNOWLEDGMENTS I would like to thank my advisor, Dr. Paul A. Moore, and the members of the Laboratory for Sensory Ecology, past and present, for their continued support and guidance throughout this project. To those who came before me, this work would not exist had I not been able to stand on your shoulders. To the lab mates who spent a summer lugging cinderblocks on the stream pad with me, I owe you my sanity. I would like to thank the constellation of scientists, mentors, and friends who comprise the University of Michigan Biological Station. Your excitement and encouragement inspired me to become a scientist. My experiences at UMBS have shaped me immeasurably, and I couldn't be more grateful. Special thanks to the Marian P. and David M. Gates Graduate Student Endowment Fund for making this research possible. I would also like to thank my committee members, Dr. Louise Stevenson and Dr. Mamadou Coulibaly, for generously sharing their expertise. You have both pushed me to reflect on my work and generate better science. Your advice has been invaluable to me throughout this endeavor. Finally, I would like to thank the friends and family who have helped me to navigate, not only my graduate studies, but life in general. Molly and Brody, thank you for being...

Spatial, but not temporal, aspects of orientation are controlled by the fine-scale distribution of chemical cues in turbulent odor plumes

“…An electrochemical detection system (Epsilon, Bioanalytical Systems, West Lafyette, IN, USA) was used to quantify the finescale distribution of a 0.001 mol l −1 dopamine tracer (see 'Odor delivery' section). This system has been used to quantify the finescale distribution of chemicals in both field and laboratory settings (Weighman and Moore, 2020;Harrigan and Moore, 2018;Edwards and Moore, 2014). A triple-carbon-fiber microelectrode was constructed in-house using standard procedures (Moore and Gerhardt, 2000;Moore et al, 1992).…”

“…We used standard methods for the quantification of chemical signals within the turbulent odor plume (Moore and Atema, 1991;Moore and Gerhardt, 2000;Edwards and Moore, 2014;Weighman and Moore, 2020). In general, DC potential amperometry was used to measure chemical concentrations arriving at the triple-carbonfiber electrode.…”